MgCl2•alcohol adducts and their use in the preparation of catalyst components for the polymerization of olefins are well known in the art.
Catalyst components for the polymerization of olefins, obtained by reacting MgCl2•nEtOH adducts with halogenated transition metal compounds, are known in the art and described for example in U.S. Pat. Nos. 4,399,054 and 6,127,304. The adducts are prepared by emulsifying the molten adduct in an immiscible dispersing medium and quenching the emulsion in a cooling fluid to collect the adduct in the form of spherical particles. The adduct generated by this process has generally a number of moles of alcohol per mole of MgCl2 of about three. The catalysts obtained by the said adducts in general display a high activity but in some cases are to be improved in terms of morphological stability. According to the teaching of the art, the morphological stability can be increased by dealcoholating to some extent the adduct so as to induce the formation of porosity. The so obtained adduct indeed produces a catalyst that may be more stable but often also less active in polymerization.
In order to create a right mix of properties WO2012/084735 teaches to prepare magnesium chloride ethanol adducts originally having 4 moles of alcohol per mole of magnesium and also containing a relatively high amount of water. The adducts are then dealcoholated to create adducts with pores having radius in a specific range size. The deriving catalyst shows indeed capability to produce polymer particles with a reduced percentage of breakages in propylene polymerization but with a bulk density still to be improved for reaching a satisfactory plant productivity. On the other hand, EP 1490416 B1 expressly teaches not to exceed 1% of water in the ethanol/magnesium chloride adduct preparation in order to have high activity. This is proved by the fact that when the amount of water is increased (comparative example 1), the polymerization activity decreased. The applicant also proved that the adducts having a limited amount of water and and least 57% bw of ethanol as taught by the cited reference do not generate catalysts with a satisfactory stability in ethylene polymerization.
It has therefore been very surprising to discover that adducts having reduced porosity and relatively low ethanol/water ratio could generate catalysts which in turn produce polymers having very high bulk density, good balance between activity and stereo specificity and high stability in ethylene polymerization.